Normal processes of cellular differentiation involve coordinated programs of tissue-specific gene expression. Recently, genome-wide approaches to mapping histone modification and transcription factor binding patterns have revealed that promoter-distal enhancer sequences exhibit the greatest variability among distinct mammalian cell types, and that they most likely represent the most significant determinant of tissue-specific gene expression. Using erythroid differentiation as a model system, we have previously investigated the phenomenon of hyperacetylated domains, which consist of broadly-distributed (>12 kb) patterns of histone modifications that are usually confined solely to the promoter-proximal regions of active genes, and we have accumulated evidence that such domains represent a function of a specific class of distal enhancer element. We are therefore interested in investigating the mechanism by which such enhancers mediate domain formation, in order to gain insight into how hyperacetylated domains contribute to tissue-specific gene activation during terminal differentiation. To do this, we will investigate candidate erythroid-specific domain-forming enhancers in detail to identify the DNA-binding factors required for their activity, and in turn the associated cofactors and histone modifying enzymes. In addition, we will define the requirements for domain formation at a gene locus active in both erythroid and liver cells, and thus determine the features common between domains in different cell types. From these studies, we hope to elucidate the specific mechanisms by which distal enhancers mediate erythroid-specific gene activation during erythroid maturation.